Police believe the men have been living in Britain for some time and were not smuggled into the country just ahead of their attempted suicide attacks.

They are believed to have family here as well as links with the the substantial Somali, Kenyan and Ethiopian communities living around London.

Appeals have been made to East African community leaders in the capital to help police in Britain’s biggest manhunt.

Until now Islamic militants from East Africa have not been heavily involved in terror cells in Western capitals.

Intelligence agencies have, however, long suspected that “sleeper cells” from the region could be in Britain awaiting their orders.

Scotland Yard is anxious not to antagonise the law-abiding communities but point out that the men could have taken advantage of the regular humanitarian crises and conflicts from their home countries like Somalia and Ethiopia to claim refugee status in the West.

Home Office figures show that 45,815 Somalians — minus dependents — applied for asylum in Britain between 1993 and 2004.

Of these, 30,875 were given asylum or allowed to stay on humanitarian grounds.

Immigration authorities say 4,635 Ethiopians applied for refugee status of whom 690 were given asylum. Failed asylum-seekers are not sent back to the two countries because of the violence and upheaval there.

The Home Office says 6,010 Kenyans applied for asylum, of whom 440 were given asylum or allowed to stay. There are no figures for how many of those refused asylum have been returned home.

Western intelligence agencies have given warning of a new generation of terror camps being set up by Islamic militant groups in the region. The FBI describe the porous borders of East Africa as “the weakest link” in their war on terror.

US agents say they have new evidence that militant groups with links to al-Qaeda have set up bases in lawless pockets of Somalia and Ethiopia, and smuggled their trained recruits in an out of Kenya.

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